Field of the Invention
The present invention relates to an electronic device, and specifically relates to an electronic device having a function of detecting degradation of a printed circuit board used for an electronic device such as a numerical control device.
Description of the Related Art
In an electric circuit and an electronic circuit used for various kinds of electronic devices, a printed circuit board is often used such that a circuit pattern composed of a conductive material is provided on a board composed of an insulative material. In the environment where a device including such a printed circuit board is used, there is a case where the printed circuit board is contaminated with powder dusts, cutting fluid and the like to suffer malfunction. In particular, when a state where the cutting fluid sticks to the printed circuit board is lasting for a long period, wires on the printed circuit board are sometimes corroded, and as a further progress of the corrosion, the wires are being broken, which causes the malfunction.
Examples of methods of detecting such degradation of the printed circuit board include the following technologies.
Japanese Patent Laid-Open No. 2009-264989 discloses a control device including a printed circuit board, including wires for detecting degradation with an interval same as or more of the minimum wire interval in the printed circuit board, a voltage application circuit that applies a defined voltage between the wires, a degradation determination circuit that is connected to the wires and detects the presence or absence of decrease in insulation resistance, an integration circuit that integrates signals obtained by detecting the presence or absence of decrease in insulation resistance, and an abnormality signal generation circuit that generates an abnormality signal corresponding to times of the integration at the integration circuit.
Japanese Patent Laid-Open No. 2006-19405 discloses a device in which, in order to enable detection of degradation and malfunction of a printed wiring board, a predetermined voltage is applied to one of input terminals of the pins of an IC and the other of input terminals is grounded. According to such connection, insulation degradation between the pins of the IC is detected.
Japanese Patent Laid-Open No. 2001-251026 discloses a device in which, for patterns at the same voltage in a part of a printed circuit board, a pattern with a width narrower than that of the other wires and a pattern narrow in insulation distance are provided. Thus, line breakage caused by corrosion of the pattern and/or short circuit caused by migration or the like are configured to occur securely earlier than the other patterns. Such patterns are implemented therein as sensors to perform automatic notification to a maintenance center or the like.
In a device for detecting insulation degradation of a printed circuit board of Japanese Patent Laid-Open No. 10-239374, electrodes are disposed on the whole surface of the printed circuit board to find insulation degradation of the printed circuit board. In the case of the insulation degradation, to set a signal generated from a microcomputer to the H-level is suspended, so that power consumption of the printed circuit board is suppressed.
In Japanese Patent Laid-Open No. 10-62476, a pattern for detecting degradation is provided to be exposed to the air on a printed circuit board of a degradation detecting device. A constant current is allowed to flow from a power supply VCC via a resistor R0 and the like, and an A/D converter detects a voltage of both ends of the pattern. A determination circuit periodically analyzes the detection voltage. When the pattern is corroded to be thin, the detection voltage of the A/D converter increases. When the detection voltage exceeds a predetermined threshold, which is transmitted to a display circuit by the determination circuit, the display circuit performs display of a warning, buzzer output thereof or the like. Upon the warning, the operator performs maintenance or replacement of the printed circuit board unit.
Japanese Patent Laid-Open No. 8-220158 discloses a device for detecting degradation of insulation along the face, the device including a pair of electrodes which are disposed to oppose the surface of an insulation plate provided on the outer face of an electric device and are connected to a AC power supply, and an insulation property detection unit that detects a current flowing between the electrodes, compares it with a preset value and outputs an alarm signal to a display unit.
Japanese Patent Laid-Open No. 7-249840 discloses a device including a printed circuit board in which plural conductors constituting a part of an electronic circuit are provided on the surface of a base board by print wiring. A pair of electrode conductors are provided in advance by print wiring to closely oppose each other without contact with each other at positions independent from the conductors constituting the electronic circuit on the surface of the base board such that there are certain resistance value and electrostatic capacity between both of them. The device predicts time to short circuit between the conductors.
Japanese Patent Laid-Open No. 2001-358429 discloses a technology in which electrode conductors for detecting degradation are formed by printing at positions independent from conductors constituting an electronic circuit, and the degradation of the conductors constituting the electronic circuit is detected on the basis of chronological change in electric characteristics measured with the electrode conductors for detecting degradation.
In the technologies disclosed in Japanese Patent Laid-Open No. 2009-264989, Japanese Patent Laid-Open No. 2006-19405, Japanese Patent Laid-Open No. 2001-251026, Japanese Patent Laid-Open No. 10-239374, Japanese Patent Laid-Open No. 10-62476, Japanese Patent Laid-Open No. 8-220158, Japanese Patent Laid-Open No. 7-249840 and Japanese Patent Laid-Open No. 2001-358429, the degradation is detected and reported on the basis of the presence or absence of decrease of the insulation resistance, the detection of the insulation degradation, the decrease of the resistance value, the detection of the current, the change in electric characteristics, and the like. However, in any of the above cases, the reference value is singular and a warning is not outputted in accordance with a plurality of degradation levels. Hence, only the notification of the presence or absence of the degradation is performed, and there is a concern that sufficient notification of the degree of degradation or the like cannot be performed.